Async error strategies

Learn different error-catching strategies for promises and async functions.

try/catch in async functions

Inside an async function, when a promise awaited with await rejects, the error is caught by the try block. You use the same try/catch structure as in synchronous code.

async function loadProfile(id) {
  try {
    const profile = await fetchProfile(id);
    return profile;
  } catch (err) {
    console.error('Loading failed', err);
    return null;
  }
}

.catch chain or try/await?

In a promise chain .catch() catches the error. In an async function try/await/catch reads more naturally. Both give the same result; you pick based on the flow.

// chain style
fetchProfile(id).catch(err => logError(err));

// async style
async function load() {
  try { await fetchProfile(id); }
  catch (err) { logError(err); }
}

Exercise Async settings loader

Write an async function loadSettings. In a try block assign the result of await fetchSettings() to const settings and return settings. In a catch (err) block call console.error(err) and return null.

Show example solution

async function loadSettings() {
  try {
    const settings = await fetchSettings();
    return settings;
  } catch (err) {
    console.error(err);
    return null;
  }
}

Test yourself

How is a rejected promise caught in an async function?
- Only with .then()
- Only with window.onerror
- Only with a finally block
- By wrapping await in try and using catch
Show answer

By wrapping await in try and using catch — Correct! You wrap await in try and catch it.

Call with await

async function loadItem() {
  try {
    const item = ____ fetchItem();
    return item;
  } catch (err) {
    logError(err);
  }
}

Show answer

async function loadItem() {
  try {
    const item = await fetchItem();
    return item;
  } catch (err) {
    logError(err);
  }
}

Match strategies to their uses

try + await + catch

Error in async function
.catch(handler)

Error in promise chain
.finally(fn)

Cleanup either way
unhandledrejection

Uncaught rejection

Next lesson: Global error handling

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